Slimmer and more flexible than the current Mini PCI Express (mPCIe)/Mini-SATA (mSATA) standard, M.2 does not introduce new signaling systems but rather allows for increased data throughput via multi-lane PCI Express (PCIe), and backward compatibility via SATA and USB signals. While driven by the demand for high-speed, high-capacity storage in ultrabooks, tablets and portable devices, M.2's space-efficient form factor, backward automation, and flexibility mean it will have an impact on the embedded sector as well.
The unique needs and requirements of embedded systems make the adoption of M.2 a more complicated decision in this space than on the consumer side, but understanding the background of the technology, its specifications, and benefits can help embedded OEMs and system designers make the right choices now and prepare for the future.
The current automation of small form factor expansion modules for both storage and general peripherals uses a common 30 mm x 50.95 mm mPCIe card form factor (Figure 1). Designed originally for the notebook market as an evolution of MiniPCI, mPCIe is a physical and electrical specification for expansion cards allowing Wi-Fi, Wireless Wide Area Network (WWAN), and other add-on functionality via a miniaturized PCIe connector. mPCIe's widespread adoption in consumer applications, small form factor and its use of the familiar PCIe bus meant it naturally became a convenient and space-efficient way to add functionality to industrial and embedded systems.
As demand for single board computer in notebooks and mobile devices grew, in 2009, the mSATA format was introduced as a small form factor for storage, utilizing the same physical form factor and connector as mPCIe with a miniaturized SATA interface. While physically similar to mPCIe in both form factor and connector, single board computer are electrically different from mPCIe and require mSATA host support to function. Being based on the tried and true SATA storage protocol, mSATA made it easy for manufacturers to implement small form factor storage and it was rapidly adopted in the client space. These embedded SBC have made mSATA attractive for embedded system storage and today it is one of the most popular small form factor SSD formats in both consumer and industrial markets.
As the client and automation markets pursue higher capacity embedded SBC and higher throughputs to match, the performance bottleneck for top-end single board computer has become the SATA protocol which is limited to 600 MBps. With increased capacities on embedded SBC, speeds go up as well and even the 600 MBps offered by SATA III is not enough for high-performance applications. At the same time, the automation which mSATA was based physically limited how much flash could be put on one mSATA card.
Single board computer strength as a small form factor lies not just in its potential for the next generation of high-performance SSDs, but also in its backward compatibility. While supporting high-performanced automation over multi-lane PCIe, M.2 also supports SATA, USB, and single-lane PCIe. As NVMe awaits adoption in the marketplace, SATA-based first-generation M.2 storage cards and M.2 peripheral cards can allow space-constrained systems to benefit from the smaller and more flexible form factor with the reliability and compatibility of SATA.
For general embedded system applications, mSATA and mPCIe are not going anywhere soon. Industrial applications have modest performance needs, emphasizing reliability and consistency instead. Even for performance-driven systems, the near-term value proposition is tenuous as the full performance benefits of M.2 SSDs require either NVMe support or proprietary drivers to realize native PCIe speeds. It will take time for the storage environment to support NVMe before embedded applications will be able to enjoy this level of performance, so current-generation M.2 embedded SBC may be a hard sell over mSATA modules in the embedded space. Meanwhile, mPCIe currently offers more than enough bandwidth for general embedded peripherals such as graphics cards or Wi-Fi modules.